Pressurized paints, more commonly referred to as aerosol paints, have traditionally been high in volatile organic content (VOC) due to both the resin systems used in the paint and the propellant systems used to expel the resin from the container. Newer VOC regulations throughout the United States of America and the world have forced manufacturers to develop alternative aerosol paint formulations which have lower VOC's. In particular, the Bay Area Air Quality Management District (BAAQMD-California), in 1990 and 1991, adopted stringent regulations regarding the allowable levels of volatile organic content in aerosol paints and coatings. For non-flat (gloss) paint products, the acceptable VOC content, expressed as a percent of volatile organic content by weight of product is 65%.
Some manufacturers, such as Page (U.S. Pat. No. 4,384,661) have attempted to formulate acceptable aerosol coating products using water as an ingredient. The present invention represents a major development in aerosol paint formulation. The present invention uses a non-aqueous dispersion as a principal resin in an aerosol paint formulation. The present invention results in a coating composition which is VOC compliant (using the BAAQMD standards), has good in-can stability and better performance properties than aqueous-based aerosol compositions. The present invention solves one of the problems associated with other attempts to formulate lower VOC aerosol products; namely, paint viscosity so high that the products will not spray in an acceptable fashion.
Non-aqueous dispersions (NAD's) are well known in the non-aerosol coatings art and typically consist of dispersions of addition polymers in a relatively non-polar non-aqueous liquid containing a steric stabilizing agent having dual affinity to both the dispersing and the dispersed media. For example, U.S. Pat. No. 3,198,759 teaches dispersions of addition polymers in a hydrocarbon medium. The hydrocarbon medium contains one or more aliphatic hydrocarbons containing dissolved therein an alkyd formed by either the direct esterification of a drying oil fatty acid with a dicarboxylic acid and a polyhydric alcohol or the indirect esterification of a drying oil by first alcoholization with a polyhydric alcohol and second esterification with a polybasic acid. European Patent Application 0 3 10 331 A2 teaches a non-aqueous dispersion of a soluble low molecular weight non-alkyd polymer which is attached or adsorbed onto a second non-soluble alkyd-free polymer. U.S. Pat. No. 4,530,957 teaches non-aqueous dispersions based on crosslinked acrylic polymer particles dispersed in a non-aqueous medium having a polymeric dispersion stabilizer. The polymeric dispersion stabilizer can be an alkyd which is formed by the self condensation of 12-hydroxystearic acid followed by a capping reaction with glycidyl methacrylate. U.S. Pat. No. 4,206,099 teaches non-aqueous dispersions of crosslinked polymer particles in a non-aqueous medium having an amphipathic steric stabilizing agent. The steric stabilizing agent can be a graft copolymer obtained by reacting a low molecular weight carboxyl group terminated condensate of linseed oil fatty acids and 12-hydroxystearic acid with acrylic copolymers. U.S. Pat. No. 3,779,977 teaches non-aqueous dispersions of an acrylonitrile copolymer in a liquid butadiene homopolymer or copolymer in a non-polar organic hydrocarbon liquid.
Previous work by Rao et al. (U.S. Pat. No. 4,983,716 has shown that selecting alkyds which have specific properties for use as the steric stabilizing media for an NAD can lead to high solids, low VOC stable NAD's which exhibit acceptable viscosities when used as non-aerosol paints and coatings. In the present invention, we have found a means for producing aerosol paint compositions using NAD's. The particular NAD's which are acceptable for use herein utilize either conventional alkyds or the alkyds taught by Rao et al. as the steric stabilizing media. These NAD's have excellent stability, filterability, gloss, low grit, viscosity and tack-free and dry hard times when formulated as air dry coating compositions. We have now been able to incorporate these NAD's into aerosol compositions to achieve a level of performance not previously associated with lower VOC aerosol paints. The NAD's used in this invention air dry faster than the alkyds used to make the NAD; consequently, they represent an improvement over traditional alkyd-based aerosol paints, as well.
The NAD's used herein utilize either conventional, traditional alkyds or the alkyds taught by Rao et al. as the dispersing media and steric stabilizer. These NAD's require a specific selection process wherein certain critical parameters, described fully below, must be observed in order to produce a NAD with a viscosity sufficiently low so as to be useful in the production of a stable, high performance, low VOC aerosol coating. Selection of the remainder of the aerosol coating, the propellant, and even the valve and actuator components is also important to produce a stable, lower VOC aerosol paint composition with acceptable spraying characteristics.